1. Field of the Invention
The present invention relates to a technique of ejecting ink droplets to implement printing.
2. Description of the Related Art
FIG. 33 shows a positional relationship between an ink ejection detector and a head in a prior art ink jet printer. In an ink jet printer with a head 801 that has a plurality of nozzle arrays 802, 808 to eject ink droplets, an ink ejection detector (a light-emitter 803 and a light-receiver 804). is generally used to detect failure of ink ejection from each nozzle, because of clogging of the nozzle or shortage of ink. In FIG. 33, 805 shows a light sensor sensitive area and the head 801 moves along an arrow 813.
The prior art ink ejection detector carries out detection of ink ejection for each nozzle. Every time failure of ink ejection is detected, because of the clogging of the nozzle, the ink jet printer requires a specific operation to prepare for resumption of ink ejection with recovery means. While in the case of shortage of ink, a new supply of ink is required for resumption of ink ejection. Accordingly a fairly long time is required to implement detection of ink ejection with regard to all the nozzles or any arbitrary nozzle array. The one-by-one nozzle detection technique takes a long time to complete detection for a large number of nozzles, and requires higher sensitivity for the ink ejection detector as nozzle density increases.
The object of the present invention is thus to provide an ink jet printer that is able to detect ink ejection from nozzles with high-accuracy.
In order to attain the above object, an ink jet printer according to the present invention comprises a carriage configured to be able to reciprocate relative to a printing medium, and a plurality of nozzle arrays mounted on the carriage to eject ink droplets, wherein the ink jet printer further comprises light detection unit scans the plurality of nozzle arrays at a predetermined angle relative to a columnar direction of the nozzle arrays, wherein the angle is attained by a clockwise or a counterclockwise rotation about a center of each nozzle array.
The light detection unit may include a light sensor that is disposed at a specific position so that light is scattered by ink droplets ejected from each nozzle array.
The light detection unit may be disposed at the predetermined angle, so that a sensitive area of the light sensor is fully utilized with regard to each nozzle array.
The light detection unit may have an optical axis arranged at a preset angle relative to a head nozzle surface.
Since the arrangement of the present invention carries out detection of ink ejection on an array-by-array basis in the ink jet printer, even if there are a plurality of nozzles that do not eject ink in one nozzle array, because of the clogging, the present invention use recovery means once for each array but not once for each nozzle, thereby shortening a time period from detection of ink ejection failure to its recovery with the recovery means.
Further, the inclination of the optical axis of the light detection unit (ink ejection detector) at the predetermined angle relative to the nozzle arrays, increases the light-shielding area of the sensor of the light detection unit. This improves the sensitivity of the sensor and effects high accuracy detection of ink ejection without requiring any highly sensitive ink ejection detector, even if there exist a large number of nozzles.
The present invention is also directed to an ink jet printer comprising a print head having a plurality of nozzles in arrays for ejecting ink droplets, a carriage for reciprocating the print head relative to a printing medium, and a light detection unit for detecting an ejection state of each nozzle, wherein the light detection unit includes a light-emitting element and a light-receiving element, where an optical axis connecting the light-emitting element with the light-receiving element is arranged at a predetermined angle relative to a columnar direction of the nozzles.
It is preferable that the light detection unit has a sensitive area within a predetermined distance from the optical axis, in which ink droplets are detected, and that the light detection unit is arranged at the predetermined angle relative to the columnar direction of the nozzles in order to cause nozzles on both ends of each nozzle array, among the plurality of nozzles, to be within the sensitive area.
The ink light detection unit may be arranged at a home position of the print head, or may alternatively be disposed on either one of the print head and the carriage with the print head mounted thereon. In the former case, it is preferable that the home position is also a position of blind ejection for recovery of the nozzles.
In order to attain at least part of the above objects, the present invention carries out inspection of nozzles for ejection of ink droplets with regard to an ink jet printer (printing apparatus) as discussed below. In the description hereof, the inspection for ejection of ink droplets is referred to as the xe2x80x98dot dropout inspectionxe2x80x99. The present invention is directed to an ink jet printer that ejects ink droplets and thereby implements printing. The ink jet printer includes a print head having a plurality of nozzles, from which ink droplets are ejected, a light detection unit (inspection unit) that has a light emitting element for emitting a light beam and a light receiving element for receiving the light beam emitted from the light emitting element and determines the active or inactive state of the nozzles based on whether or not the light beam is intercepted by ink droplets, and a carriage (feeding mechanism) that moves at least one of the print head and the light detection unit, so as to move the print head relative to the light detection unit. At least part of the plurality of nozzles are inspected while the print head moves relative to the light detection unit.
This arrangement ensures the higher-speed inspection of the plurality of nozzles for ejection, compared with the prior art structure that carries out the inspection for ejection while the light detection unit and the print head are at a stop. This accordingly shortens the time period required for the inspection for ejection. In the prior art structure that repeats the feed and the stop of the light detection unit or the print head for the inspection of the plurality of nozzles for ejection, the repeated feed and stop may increase the mechanical errors. The arrangement of the present invention, however, carries out the inspection of the plurality of nozzles for ejection of ink droplets while either the light detection unit or the print head is moved, thereby having no such problems.
It is preferable that the print head moves relative to the light detection unit at a fixed speed. In this arrangement, the timecan be readily estimated, when an ink droplet passes through the light beam in the process of inspection for ejection of ink droplets.
In one preferable application of the present invention, the plurality of nozzles constitute at least one nozzle array and arranged in the array at a fixed nozzle pitch in a predetermined alignment direction. In this application, the light beam is emitted in a specific direction having an angle xcex8 relative to the predetermined alignment direction (where xcex8 is greater than 0 and less than 180 degrees). It is further preferable that ink droplets are ejected towards the light beam while the print head is moving relative to the light detection unit at the fixed speed.
In this application, the movement of either the print head or the light detection unit causes the nozzle array to relatively pass through the light beam having the predetermined angle xcex8 relative to the nozzle array. In the case where the alignment direction of the nozzle array is coincident with the optical axis of the light beam, all the nozzles included in the nozzle array simultaneously intersect the optical path of the light beam. The preferable application of the present invention, however, keeps the optical axis at the predetermined angle relative to the nozzle array, so that the respective nozzles included in the nozzle array sequentially intersect the optical path of the light beam. In this arrangement, the respective nozzles can be inspected sequentially for ejection.
In another preferable application of the present invention, all nozzles included in one specific nozzle array to successively eject ink droplets in the inspection from an intersection of the light beam with an ink droplet ejected from a nozzle at one end of the specific nozzle array to an intersection of the light beam with an ink droplet ejected from a nozzle at the other end of the specific nozzle array. In this application, it is preferable that the ink jet printer satisfies:
sinxcex8 less than La/D, CRV/Fxe2x89xa6La/cosxcex8
where D denotes the nozzle pitch in the predetermined alignment direction, La denotes a width of the light beam emitted from the light emitting element, CRV denotes a moving speed of the print head relative to the light detection unit, and F denotes a frequency of ejection of ink droplets.
It is more preferable that the ink jet printer satisfies:
sinxcex8 greater than La/D, CRV/Fxe2x89xa6La/cosxcex8.
In still another preferable application of the present invention, the plurality of nozzles constitutes in a plurality of nozzle arrays. In this application, it is preferable that the ink jet printer satisfies:
tanxcex8 greater than LD/(Dxc3x97(Nxe2x88x921))
where LD denotes an interval between adjoining nozzle arrays and N denotes a number of nozzles included in each nozzle array.
It is more preferable that the ink jet printer satisfies:
tanxcex8xe2x89xa6LD/(Dx(Nxe2x88x921)).
In accordance with one preferable embodiment of the present invention, the plurality of nozzles are classified into a plurality of inspection groups. One inspection group is selected from the plurality of inspection groups, as an object to be inspected, so that and the selected inspection group is inspected during one pass of movement of the print head relative to the light detection unit in a predetermined direction.
This arrangement enables the inspection to be carried out with high accuracy even when it is impossible to inspect all the nozzles on the print head by one pass of movement of the print head or when the accuracy of inspection is lowered in the case of inspection of all the nozzles by one pass of movement. The structure of this embodiment classifies the nozzles into the plurality of inspection groups and carries out the inspection for each inspection group. This enables the time period required for the inspection of nozzles for ejection to be divided into short time periods, and does not require any collective long time. Another required work may be interposed between the inspection of the respective inspection groups for ejection according to the requirements.
It is preferable that the plurality of nozzles are classified so that ink droplets ejected from two or more nozzles included in one identical inspection group do not simultaneously intercept the light beam emitted from said light emitting element. This arrangement enables all the nozzles included in one inspection group to be inspected for ejection of ink droplets during one pass of movement of the print head or the light detection unit.
In accordance with another preferable embodiment of the present invention, the plurality of nozzles constitutes in a plurality of nozzle arrays, and the plurality of nozzles are classified so that each of the plurality of inspection groups includes nozzles that are periodically selected at a ratio of one every n nozzles (where n is an integer of at least 2) out of at least one nozzle array among the plurality of nozzle arrays. The xe2x80x98inspection groupxe2x80x99 is not required to have its constituents, that is, nozzles, in all the nozzle arrays on the print head.
In this embodiment, there is a sufficient interval between adjoining nozzles in one identical inspection group. Even when the width of the light beam emitted from the light emitting element is large relative to the nozzle pitch, this arrangement desirably reduces the possibility of confusion of ink droplets ejected from the adjoining two nozzles in the same inspection group in the process of the inspection and effectively prevents the mistakes in the inspection.
It is preferable that each of the plurality of inspection groups includes nozzles that are selected from nozzle arrays, which are periodically selected at a ratio of one every m nozzle arrays (where m is an integer of at least 2) among the plurality of nozzle arrays. The xe2x80x98inspection groupxe2x80x99 is not required to have, as its constituents, all the nozzles included in the nozzle array that satisfies the above condition.
In the event that the gradient of the optical axis is large relative to the interval between adjoining nozzle arrays, the locus of an ink droplet ejected from a nozzle in one nozzle array may simultaneously pass through the light beam while the locus of an ink droplet ejected from the last nozzle in an adjoining nozzle array passes through the light beam. In the above application of the present invention, however, there is a sufficient interval between the adjoining nozzle arrays in one identical inspection group. This arrangement desirably reduces the possibility of confusion of ink droplets ejected from the nozzles in the adjoining two nozzle arrays in the same inspection group in the process of the inspection and effectively prevents the mistakes in the inspection.
In another preferable application of the present invention, different priorities corresponding to a sequence of execution of the inspection are allocated to the plurality of inspection groups. The plurality of nozzles are classified so that the inspection group having the higher priority number include a greater number of nozzles. This application may reduce the total number of inspection groups, compared with the uniform classification method that selects one nozzle out of n nozzles and accordingly classifies the nozzles into n inspection groups.
In accordance with one preferable embodiment of the present invention, the print head is driven by the carriage to move bi-directionally in a main scanning direction. A movable range of the print head in the main scanning direction includes a printing area, in which the print head causes the plurality of nozzles to eject ink droplets so as to implement printing on the printing medium, and an adjustment area, in which the inspection of the plurality of nozzles for ejection of ink droplets and a flushing operation of the plurality of nozzles are carried out. In this embodiment, it is preferable that the inspection for ejection is carried out in the adjustment area, prior to the flushing operation, at a time point when the print head reaches the adjustment area after execution of the printing in the printing area and before the print head returns from the adjustment area to the printing area.
This arrangement enables the printing to be implemented immediately after the flushing operation without the inspection for ejection. This desirably prevents the non-smooth ejection of ink and the curved flight of ink droplets, which are due to the increased viscosity of ink by the elapse of time used for the inspection.
It is alternatively preferable that the inspection of one of the inspection groups for ejection is carried out in the adjustment area respectively in a forward pass and a backward pass the print head, at a time point when the print head reaches the adjustment area after execution of the printing in the printing area and before the print head returns from the adjustment area to the printing area.
This arrangement enables inspection of the inspection groups to be carried out respectively in the forward pass and in the backward pass of the print head between the printing operations in the printing area. This ensures the inspection of the respective nozzles for ejection at relatively short cycles. This application accordingly prevents the possible failure of ejection of ink droplets between the inspections and ensures the high picture quality of the resulting prints.
When the printing is not carried out in the printing area in either the forward pass or the backward pass of the print head, the print head may be fed at a higher speed in the pass on which the printing is not executed, than in the other pass. The inspection for ejection is carried out in the pass, on which the print head is fed at the higher speed, it is preferable to lower the feeding speed of the print head to a specific level suitable for the inspection, prior to the inspection.
This arrangement feeds the print head at the higher speed in the pass on which the printing is not executed, thereby shortening the total time period required for printing. When the inspection for ejection is carried out, the feeding speed of the print head is lowered to ensure the required accuracy for the inspection.
The principle of the present invention may be actualized by a variety of applications given below:
(1) printing apparatus, print control apparatus;
(2) method of printing, method of control printing;
(3) computer programs to realize the above apparatuses and the methods;
(4) recording media, on which computer programs realizing the above apparatuses and the methods are recorded; and
(5) data signals embodied in a carrier wave and including computer programs realizing the above apparatuses and the methods.